The paper explains response particles like yes and no as anaphoric elements that pick up propositional discourse referents that are introduced by preceding sentences. It is argued that negated antecedent clauses introduce two propositional discourse referents, which results in ambiguities of answers that is partly resolved by pragmatic optimization. The paper also discusses response particles like okay, right and uh-huh and uh-uh, and German ja, nein and doch.